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Microbiology > Chapter 13- Control of microbial growth > Flashcards

Chapter 13- Control of microbial growth Flashcards

1
Q

Microbial spectrum

A

Refers to how many different types of microorganisms an antimicrobial kills

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2
Q

How clean is clean?

A

Clean is a relative term. Whether an object or surface is “clean enough” depends on its intended use. Microbial load can be reduced by washing, vacuuming, and dishwashing

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3
Q

What are the negative impacts of sterilization?

A

Requires time, is labor intensive, can degrade the quality of the item being treated, or have a toxic effect on users

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4
Q

CDC biosafety levels are ranked by

A

The severity of disease and ease of transmission. There are 4 levels

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5
Q

BSL-1

A

Microbes are not known to cause disease in healthy hosts and pose minimal risk to workers and the environment. Non Pathogenic strains of E. coli is an example, along with viruses that infect animals other than humans. Few precautions are necessary

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6
Q

BSL-2

A

Microbes are typically indigenous and are associated with diseases of varying severity. They pose a moderate risk. PPE (lab coat, gloves) are necessary if working with these organisms in the lab, along with an eyewash station and autoclave. Staphylococcus aureus is an example, mumps and measles viruses.

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7
Q

BSL-3

A

Microbes are indigenous or exotic and cause serious or potentially lethal diseases through respiratory transmission (inhalation). Individuals need to work in biosafety level labs to prevent transmission. Individuals must wear a respirator.
Mycobacterium tuberculosis is an example, so is HIV. Treatment exists for diseases categorized at levels 2 and 3

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8
Q

BSL-4

A

Microbes are dangerous and exotic, posing a high risk of aerosol-transmitted infections, which are frequently fatal without treatment or vaccines. Few labs are at this level, because they require full PPE (full body suits) and for the lab to be sealed and under negative pressure. Individuals must shower and change clothes when exiting. Ebola and Marburg viruses are examples. Typically, there is no treatment for these organisms

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9
Q

Sterilization

A

Process by which all living cells, spores, and viruses are destroyed on an object. This is done in medical, laboratory, manufacturing, and food industry settings

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10
Q

Disinfection

A

The killing or removal of disease producing organisms from inanimate surfaces. It does not necessarily result in sterilization because endospores can remain. Vinegar is a natural disinfectant due to its acidity, while chlorine is a chemical disinfectant used on surfaces

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11
Q

Antisepsis

A

Similar to disinfection but applies to removing pathogens from the surface of living tissues, such as the skin

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12
Q

Antiseptic

A

A chemical agent that can be safely used externally on living tissues to destroy microorganisms or inhibit its growth. Neosporin or iodine is an example. Must be able to penetrate deeply without causing tissue damage

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13
Q

Sanitation

A

Consists of reducing the microbial population to safe levels and usually involves cleaning an object as well as disinfection. Used for food handling equipment and reduces bacterial numbers to meet public health standards. Includes dishwashers, which use hot water and air, resulting in the death of microbes through high temperatures. Hospitals use chemical disinfectants for sanitation

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14
Q

2 classes of antimicrobials

A
  1. Cidal agents
  2. Static agents
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15
Q

Cidal agents

A

Kill microbes. Bactericidal, algicidal, fungicidal, virucidal, depending on what type of microbe is killed

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16
Q

Static agents

A

Inhibit or control growth. Bacteriostatic, algistatic, fungistatic, virustatic, depending on what type of microbe is inhibited. These agents are less toxic to humans and can better preserve the integrity of the item that is treated. In an otherwise healthy individual, static agents can be used to treat an infection. The immune system will do the rest of the work to clear the infection

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17
Q

How are disinfectants selected?

A
  1. Must be fast acting in the presence of organic materials
  2. Must be effective against all microorganisms without destroying tissue or acting as a toxin if ingested
  3. Easily penetrate the material to be disinfected without discoloration or damage
  4. Easy to prepare and stable in the environment where it is to be used
  5. Inexpensive and easy to use
  6. Not have an unpleasant odor
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18
Q

Microbial death curve

A

Demonstrates the progress and the effectiveness of a disinfectant- shows how many microbes have been killed. When exposed to a microbial control protocol, a fixed percentage of microbes will die regardless of the population size. Therefore, the percentage of microbes killed is more useful information than the actual number. The curve is plotted as a semilog plot

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19
Q

Decimal reduction time (D value)

A

The amount of time it takes for a specific
protocol to produce a one order-of-magnitude decrease in the number of organisms, or the death of 90% of the population. Ideally, you want at least 90% of the population to be killed

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20
Q

Factors that influence the speed at which lethal damage accumulates (6)

A
  1. The initial population size
  2. Population composition
  3. Agent concentration or dose of radiation- too high of a concentration is toxic and can degrade the materials
  4. Duration of exposure to the disinfecting agent
  5. Presence of organic material (blood, feces) that can inhibit disinfectant action, organic load
  6. Biofilm formation
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21
Q

How does population size influence the effectiveness of a disinfectant?

A

The larger the population, the longer it takes to decrease it to a specific number

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22
Q

How does population composition influence the effectiveness of a disinfectant?

A

Are spores involved? Different types of microbes need different exposure times to the disinfectant

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23
Q

Physical control measures (4)

A
  1. Temperature extremes
  2. Pressure (usually combined with temperature)
  3. Filtration
  4. Radiation
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24
Q

What type of heat is very effective at killing microbes?

A

Moist heat. Heat is the preferred sterilizing agent as long as it doesn’t damage the materials. Heat alters the membranes of microbes and denatures their proteins. Boiling is one example, but it is less effective against endospores and at higher altitudes

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25
Q

Why is dry heat sometimes used to kill microbes?

A

Dry heat is less effective, but sometimes required- moist heat can oxidize certain materials. Dry heat takes longer to penetrate the cells, so it’s much slower. Examples include incineration or a dry heat sterilizer like an oven

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26
Q

Steam autoclave

A

Uses a combination of heat and pressure to kill spores and thermophiles. Standard autoclave conditions are 121℃ at 15 psi (pounds per square inch) for 20 minutes. Uses moist heat and is considered the most effective method of sterilization

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27
Q

Thermal death point (TDP)

A

The lowest temperature that kills all the bacteria in a 24 hour culture after a 10 minute exposure. Some organisms are more heat tolerant than others

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28
Q

Thermal death time (TDT)

A

Time required to kill all the bacteria in a culture at a specified temperature

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29
Q

Decimal reduction time (D value)

A

Length of time required to kill 90% of the organisms in a population at a specific temperature

30
Q

How do autoclaves work?

A

In an autoclave, steam is supplied to a chamber from an external boiler and increases the chamber’s temperature. Autoclaves will sterilize any materials that are inside the chamber. It usually requires at least 20 minutes, but the length of exposure depends on the volume and nature of the material being sterilized. The temperature must be high enough to kill endospores

31
Q

Pasteurization

A

The goal of pasteurization is not to sterilize, but to kill pathogens without affecting the texture, color, or taste of the product. It gets rid of microbes or reduces the bacterial load so the food won’t spoil. Includes 3 different time and temperature combinations

32
Q

Low temperature, long time (LTLT) pasteurization

A

63℃ for 30 minutes

33
Q

High temperature, short time (HTST) pasteurization

A

Also called flash pasteurization. 72℃ for 15 or 16 seconds

34
Q

Ultra high temperature pasteurization

A

138℃ for 2 seconds. Produces sterilized products that can be stored without refrigeration for 6 months

35
Q

3 types of pasteurization

A
  1. Low temperature, long time
  2. High temperature, short time
  3. Ultra high temperature
36
Q

What is the point of refrigeration or freezing?

A

It is excellent to preserve food and other materials. It slows down food and other materials, but does not effectively kill microorganisms. Microbes can also be stored in this way. Temperatures between 0 and 7 degrees Celsius inhibits microbial metabolism and slows their growth

37
Q

Freeze drying

A

The use of cold temperatures and drying at the same time. Many microbes are sensitive to drying, but many are not-some microbes can be killed this way. Freeze drying is used for storing many microbes

38
Q

Filtration

A

A method of removing microorganisms from a solution. Many drugs/chemicals are sensitive to heat or other chemical sterilization methods. These solutions can be sterilized by passing them through sterile filters with tiny pore sizes that sift microbes out of the fluid. Air can also be sterilized through filtration

39
Q

What size are the pores in filtration?

A

Membrane filtration through micropore filters out of .2 micrometers can remove microbial cells, but not viruses, from solutions. To remove viruses, pore sizes of 20 nanometers are necessary

40
Q

Sonication

A

High frequency ultrasound waves that disrupt cell structures due to changes in pressure in the cytoplasmic liquid. It forms bubbles and causes the cell to lyse. This method may be able to be used in humans to treat bacterial infections. Currently used to sanitize hospital equipment and tools

41
Q

Irradiation

A

Method in which objects are bombarded with high energy electromagnetic radiation. Foods do not become radioactive when irradiated, and any reactive molecules produced when high energy particles are absorbed by food dissipate almost immediately. Includes non-ionizing radiation, ionizing radiation, and microwave radiation.

42
Q

Non-ionizing radiation

A

Ultraviolet light is non-ionizing radiation. Only effective to sterilize surfaces because it doesn’t penetrate very well. It is used to control microbial growth, but cells need to be exposed directly to the light source for mutations to be induced

43
Q

Ionizing radiation

A

Gamma rays, electron beams, X-rays are ionizing radiation. These rays are strong enough to enter the cell. Damage DNA and can generate peroxides in the cells, which can cause mutations. It can penetrate paper and plastic and can be used to sterilize lab materials that can’t be autoclaved

44
Q

Microwave radiation

A

Microwave radiation can be used for irradiation, but it does not sterilize materials. It is only effective when water molecules are present

45
Q

Efficacy of a chemical agent depends on (4)

A
  1. The presence of organic matter
  2. The kinds of organisms present- should be effective against a broad range
  3. Corrosiveness- should not corrode the surface
  4. Stability, odor, and surface tension
46
Q

What type of surface tension should a chemical agent have?

A

Low surface tension

47
Q

Commercial disinfectants are all used to

A

Reduce or eliminate microbial content from commercial products

48
Q

Ethanol, iodine, chlorine

A

Highly reactive compounds that oxidize cellular components and damage proteins, lipids, and DNA. They can be used topically but can cause staining or skin irritation

49
Q

Surfactants

A

Includes soaps and detergents and lowers the surface tension of water. Soaps can interact with nonpolar oils and grease to create emulsions in water and loosen dirt and microbes. Help in the mechanical removal of microbes from surfaces, but do not kill or inhibit microbial growth

50
Q

Aldehydes

A

Combine with and inactivate proteins and nucleic acids by replacing hydrogen atoms with alkyl groups. Formaldehyde is an example- it kills bacteria, viruses, fungi, and endospores

51
Q

Phenolics

A

Phenols have a benzene ring with an -OH group. Denature proteins and disrupt membranes, mouthwashes and throat lozenges are phenolic derivatives. Carbolic acid was one of the first disinfectants used as is a phenol. First used by British surgeon Joseph Lister on surgical wounds, but we know today that it’s an irritant

52
Q

Heavy metals

A

Bind to proteins and inhibit enzymatic activity. A small amount of heavy metal ions strongly bind to sulfur-containing amino acids and accumulate in the cells, so the metals reach high concentrations. This causes the proteins to denature. They can also be toxic to human cells. Copper, found in door handles, is one example. So is silver

53
Q

Peroxygens

A

Strong oxidizers, produce free radicals that damage cellular macromolecules. Hydrogen peroxide is an example- it is a broad spectrum disinfectant and can be used as a gaseous agent

54
Q

When is gas sterilization used?

A

Disposable plasticware such as petri dishes, syringes, sutures, and catheters are not amenable to heat sterilization or chemical disinfection. These types of products are best sterilized by gamma irradiation or antimicrobial gasses, like ethylene oxide (EtO)

55
Q

How does gas sterilization work?

A

Destroys proteins by alkylation. Microbicidal/sporicidal. Rapidly penetrates packing materials, including plastic wraps, and is highly explosive

56
Q

When is it difficult for bacteria to develop resistance to disinfectants?

A

It’s difficult for bacteria to develop resistance to chemical agents that have multiple targets and can easily diffuse into a cell (iodine)

57
Q

When is resistance to disinfectants more likely?

A

Disinfectants that have multiple targets at high concentrations may only have a single target at low concentrations- a situation that can foster resistance (triclosan).

58
Q

Fomites

A

Inanimate items, such as doorknobs, toys, or towels, which may
harbor microbes and aid in disease transmission

59
Q

2 factors that influence the level of cleanliness required for a fomite

A
  1. Its intended use- surgical instruments require a higher level of cleanliness because they are being inserted into the body
  2. The level of resistance to antimicrobial treatment by potential pathogens. Some organisms can only be killed by extreme temperatures and pressures
60
Q

Indigenous pathogens

A

Pathogens that are commonly found in that geographical area

61
Q

Exotic pathogens

A

derived from a foreign location

62
Q

Sterilants

A

Chemicals that can be used to achieve sterilization. They effectively kill all microbes and viruses, and, with appropriate exposure time, can also kill
endospores.

63
Q

Aseptic technique

A

Used in clinical settings, necessary to prevent contamination of sterile surfaces. Aseptic technique involves a combination of protocols that collectively maintain sterility, or asepsis. Aseptic technique must be used during procedures to prevent infection

64
Q

What determines whether an agent is bacteriostatic or bactericidal?

A

Factors that determine whether a particular treatment is -cidal or -static include the types of microorganisms targeted, the concentration of the
chemical used, and the nature of the treatment applied.

65
Q

Axes of a microbial death curve

A

2 variables- the reduction of microorganisms (y axis) over time (x axis), the graph is logarithmic

66
Q

When was pasteurization developed?

A

Developed by Louis
Pasteur in the 1860s as a method for preventing the spoilage of beer and wine.

67
Q

High pressure processing

A

Used to kill bacteria, yeast, molds, parasites, and viruses in foods while maintaining food
quality and extending shelf life. The application of high pressure between 100 and 800 MPa (sea level atmospheric pressure is about 0.1 MPa) is sufficient to kill vegetative cells by protein denaturation, but endospores may survive these pressures. It is not commonly used for disinfection or sterilization of fomites

68
Q

Desiccation (dehydration)

A

All cells require water for their metabolism and survival. Drying controls microbial growth, but might not kill all microbes or their endospores, which can start growing under more favorable conditions

69
Q

Lyophilization

A

A method of desiccation where an item is rapidly frozen and placed under vacuum so that water is lost by sublimination. It combines exposure to cold temperatures and desiccation to control microbial growth. It better preserves the item’s original qualities and causes less damage than conventional desiccation

70
Q

Water activity

A

The water content of food and materials. It can be lowered by adding high concentrations of solutes like salt or sugar. Water will be drawn from an area of low solute concentration (inside the cell) to an area of high solute concentration (outside the cell). Many microorganisms do not survive these conditions of high osmotic pressure, although molds and yeasts may be more tolerant

71
Q

Alcohols

A

They rapidly denature proteins, which inhibits cell metabolism. They also disrupt membranes, which causes cell lysis. They are typically used and are most effective at concentrations of about 70% aqueous solution. They are bactericidal, fungicidal, and viricidal for enveloped viruses only

Microbiology (19 decks)

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